When rating the service brake system of a motor vehicle, it is important to dimension the brake force component of the rear axle by various measures in such a manner that the rear axle will principally block later than the front axle up to a braking pressure that corresponds to a longitudinal deceleration of roughly 0.8 g. Only in the presence of a longitudinal deceleration still greater than 0.8 g or a corresponding braking pressure is it allowable that the wheels of the rear axle lock before the wheels of the front axle.
Mechanical/hydraulic pressure controllers (load-responsive controllers or controllers with a fixed change-over point) on the rear axle that were used for brake force reduction had to satisfy this demand until the introduction of anti-lock control systems (ABS).
A few years ago, a control function has been developed and introduced, above all in front-wheel driven small vehicles having an unfavorable weight distribution (much load on the front axle, little load on the rear axle), which obviated the need for hydraulic/mechanical measures to reduce the brake force component of the rear axle. This control function allowed replacing the various hydraulic/mechanical brake force controllers. The name given to this control function was ‘EBV control’ (electronic control of brake force distribution).
In a braking operation, the EBV system shuts off the rear axle (under certain circumstances, also one single rear wheel) due to the slip on at least one rear wheel from further pressure build-up by activating the inlet valves. Instead of the slip signal, various other signals, such as signals of longitudinal or transverse acceleration or derivatives and linkages thereof can be evaluated for this purpose. The rear-wheel brakes are not isolated completely from further pressure build-up, rather, a controlled pressure build-up with an extremely low gradient is permitted.
When an EBV control operation commences, further pressure build-up on the rear axle is initially prevented. The pressure can be cautiously increased at a later point of time after slip has been reduced. This arrangement develops an independent control ensuring the brake force distribution between the front axle and the rear axle without additional mechanical/hydraulic elements.
However, it cannot be ruled out that EBV control is triggered already when a harmless road irregularity or a small area of a different coefficient of friction at a relatively low braking pressure occurs, where a limitation of the brake force on the rear axle is not appropriate. When the driver is now confronted with an emergency situation demanding a maximum deceleration, i.e. a maximum utilization of the coefficient of friction on both axles, the brake force component of the rear axle can be made use of only more or less delayed.
The EBV control measures known in the art principally suffer from the following disadvantages:                The braking power of the vehicle at a rapid increase of the initial pressure is impaired because the vehicle is generally slowed down until standstill before the rear axle reaches the full rate of utilization of its braking potential;        The insufficient utilization of the braking potential of the rear axle causes increased pad wear at the front axle.        
Determining the proper point of time of the entry into EBV control represents a major problem. If EBV control is triggered as a result of a disturbance, this can eventually cause a significantly longer stopping distance.